The present invention relates to elevator braking systems. More particularly, the present invention relates to a rotary actuator that replaces a conventional elevator governor and maintains the function of the governor. The invention provides the actuation that allows a braking system to prevent the elevator car from overspeeding.
Elevator systems generally comprise an elevator car suspended by a rope system including a traction drive. The car is guided along guide rails so that relatively little lateral motion is imparted to the car during use. In passenger elevators, at least, it is conventional to provide a braking system to halt the elevator car in the event of an overspeed condition. Braking systems include actuation devices commonly known as governors.
Most elevators of the prior art employ governors. In such an elevator system, the governor detects an excessive speed of the car and actuates emergency stop devices in the event the car experiences an overspeed condition. Conventional governors include a governor pulley at an upper end of the governor system, a tension sheave at the lower end of the governor system, and an endless governor rope passed around and between the pulley and the sheave and extending substantially throughout the length of the governor system. A part of the governor rope is connected to a safety link that is mounted on the car frame. As the car ascends or descends, the governor rope travels so that the governor pulley is rotated.
In an elevator constructed in this manner, if the car travels at a speed higher than the predetermined speed for any reason, the governor pulley correspondingly rotates at a speed higher than its predetermined speed. As the governor pulley rotates at this higher speed, paired flyweights or flyballs rotating on a spindle are accelerated outwardly by centrifugal force. As the flyweights or flyballs are accelerated outwardly, an overspeed switch is tripped and power is removed from the machine motor, a brake is actuated, and, if further overspeed occurs, a clutching device is activated that will clamp down on the governor rope to activate the safeties. The result is that the elevator is brought to an abrupt, although safe, halt.
If the path of the elevator is very long, a very long governor rope is required. As the rope length increases, both the weight of the rope and the force of inertia produced during acceleration of the rope increase. Consequently, as these things increase, so does the requirement for larger and more powerful equipment to slow down the governor rope. Likewise, larger equipment would require more space.
More modern governing devices omit the stationary governor pulley and rope and fit each elevator car with its own smaller governor. Nakagawa, in U.S. Pat. No. 5,377,786, discloses a governor that includes a rotating member mounted on an elevator car so as to rollably contact the guide rail along which the elevator travels. This rotating member is looped by a belt to an actuator means which actuates the stop mechanism when the rotating speed of the rotating member exceeds a predetermined speed.
The present invention is drawn to a rotary actuated overspeed safety device for elevators. The rotary actuated overspeed device comprises a pair of pivotally mounted counterweights fixedly attached to a wheel that rollably engages an elevator guide rail. The pair of counterweights is positioned in a parallel planar relationship with the wheel. Centrifugal force causes the pivotally mounted counterweights to pivot outward toward the edge of the wheel as the wheel spins. An elevator safety is triggered when the pivotally mounted counterweights engage a clutch housing that is movably connected to the elevator safety.
A pivotally attached connecting rod may connect the pair of counterweights. This rod causes the counterweights to pivot in unison. One of the counterweights is spring-biased against an application of centrifugal force. Springs of various spring rates can be used to adjust the amount of centrifugal force needed to cause the counterweights to pivot.
The counterweights may be pivotally mounted on a base. This base is preferably positioned in a parallel planar relationship with the wheel and is fixedly connected to the wheel. The base is rotatably supported within the clutch housing by bearings. Bearings may be interposed on the base plate beneath the counterweights to facilitate the pivoting of the counterweights.
The clutch housing is movably connected to an arm that causes the elevator safety to engage when torque is transferred from the moving counterweights to the clutch housing. The clutch housing is dimensioned, configured, and positioned to be engaged by the counterweights when the counterweights pivot outwardly.
The invention also comprises a rotary actuated safety device having a wheel that rollably engages a guide rail, two pairs of pivotally mounted counterweights, and a clutch housing to actuate an elevator safety. This embodiment is substantially the same as the previous embodiment; however, the second pair of counterweights is configured to pivot under an application of centrifugal force caused by overspeed rotation in the opposite direction.